Asthma affects over 300 million individuals worldwide. MicroRNAs (miRNAs) are small noncoding ribonucleic acids (RNAs) that regulate protein synthesis by way of gene trans-repression or RNA silencing. A growing number of studies demonstrate that miRNAs control signaling pathways in every cell type and regulate inflammation. Thus, miRNAs likely play a profound role in the pathogenesis of, and susceptibility to, asthma. Early miRNA studies have identified several miRNAs associated with asthma. The presence of miRNAs stably expressed in blood indicates that miRNAs may be used as noninvasive biomarkers of asthma susceptibility and resilience. The major goal of this project is to formulate a predictive biomarker test for asthma incidence and resilience based on circulating miRNAs. To accomplish this, we have specified three coordinated specific aims. The first aim evaluates data from the genome-wide sequencing of miRNAs in the serum of 139 children from Project Viva with a history of recurrent wheezing and determines association with the subsequent asthma susceptibility and resilience four years later. The miRNA markers will then be incorporated into a predictive set of miRNA using a Bayesian network approach. The second aim seeks to prospectively validate the predictive test in an independent population of children with a history of recurrent wheezing participating in the Vitamin D Antenatal Asthma Reduction Trial (VDAART). Serum is currently available from early childhood and asthma incidence outcomes will be measured over the next three years. The Bayesian predictive miRNA models developed in Project Viva will be tested in VDAART and refined if necessary. Longitudinal miRNA measurements will permit direct asthma resilience vs. asthma susceptibility testing to assure that the predictive miRNA remain biologically relevant. Our final aim will be to interrogate the joint effects of vitamin D, which also has potential biomarker potential for asthma susceptibility, and the measured miRNA on asthma susceptibility and resilience. This will be done via statistical modeling within Project Viva and VDAART, as well as via using miRNA mimics and inhibitors and vitamin D on airway derived smooth muscle and epithelial cells. By examining changes in gene expression, a mechanistic understanding for the observed clinical associations can be garnered. We believe that these findings will uncover the role of miRNAs in asthma susceptibility and resilience and will lead to novel interventions, including miRNA targeting, to predict and alleviate this major health care problem.